In an ordinary sewing machine, there are arranged a thread take-up lever mechanism to be driven in an arm by a spindle, a thread take-up lever mechanism and a needle bar drive mechanism. A thread take-up lever is partially protruded from a vertical slit in an arm head and is reciprocally driven up and down. The arm is provided with a thread bobbin mount on its upper end side, with a thread tension regulator and a thread tension spring on its front face side and with a tension dial for a thread tension regulator near the thread tension regulator. A needle bar protrudes downward of the arm head, and a needle is attached to the lower end portion of the needle bar. A presser foot for pressing a cloth to be sewn and a presser bar for supporting the presser foot can be switched between a bottom position, at which the cloth is pressed by a lifting lever, and an upward retracted position.
In case the sewing is interrupted to exchange the thread bobbin, the presser foot is at the retracted position, and the thread tension regulator is in a released state. In this state, the thread bobbin is exchanged, and the needle thread fed out from the thread bobbin is guided through a plurality of thread guides to the thread tension regulator. The thread is engaged between a pair of thread tension discs in the released state, with a thread tension spring and further with a thread guard of the thread take-up lever. After this, the needle eye of a needle is threaded with the end portion of the needle thread. When the thread bobbin of the needle thread is to be thus exchanged, the thread is engaged with the thread tension regulator, the thread tension spring and the thread guard of the thread take-up lever and is introduced into the needle eye.
U.S. Pat. No. 3,749,039 discloses the technique, in which the threading is simplified by mounting the needle thread cassette removably on the arm. At a substantially transverse center portion of the arm of the sewing machine, there is disposed the cassette mount, in which the needle thread cassette can be removably mounted from above. This cassette mount is formed on the right side of a thread take-up lever travel space, in which the thread take-up lever of the thread take-up lever mechanism can travel reciprocally up and down, and the leading end portion of the thread take-up lever penetrates into the left end portion of the cassette mount and travels reciprocally up and down.
This needle thread cassette disclosed in U.S. Pat. No. 3,749,039 includes a cassette case having a generally trapezoidal shape, as viewed in a front elevation, and this cassette case is constructed of a case body and an openable cover. The thread bobbin is so housed in its housing portion at the upper portion in the cassette case with its axis being horizontal, and its needle thread is fed out substantially horizontally rightward by a predetermined length. The cassette case is provided in the lower portion of its center portion with a first notch for penetrating the thread tension regulator and in the lower portion of its left end portion with a second notch for introducing the thread take-up lever.
There are provided five thread guide portions for guiding the needle thread fed out from the thread bobbin. The first thread guide portion is disposed in the upper portion of the right end of the cassette; the second and third thread guide portions are disposed at positions interposing the first notch; and the fourth and fifth guide portions are disposed at positions interposing the second notch. The first thread guide portion is provided with a first resistance applying portion for applying the resistance to the needle thread, in the state where the needle thread cassette is not mounted in the cassette mount, and for releasing the resistance after the cassette was mounted. The fifth thread guide portion is provided with a second resistance applying portion for applying the resistance to the needle thread, in the state where the cassette is not mounted, and for releasing the resistance after the cassette was mounted. This second resistance applying portion applies a higher resistance than that of the first resistance applying portion.
At the left end portion of the cassette mount disposed in the arm, there is provided a thread guide member for guiding the needle thread to the thread guard of the thread take-up lever when the needle thread cassette is to be mounted. This thread guide member is made by forming a pair of left and right arm plates and a web integrally. On the rear ends of the paired arm plates, there are formed guide faces for guiding the needle thread, and notches (or cut-off portions) corresponding to the thread guard of the thread take-up lever are formed in those arm plates. At the needle thread cassette and the cassette mount, moreover, there is provided a mechanism for bringing the paired thread tension discs of the thread tension regulator into an open state, when the needle thread cassette is mounted, and for closing the paired thread tension discs after the needle thread cassette was completely mounted.
In case the needle thread cassette is to be mounted in the cassette mount, the spindle is manually turned at first to move the thread take-up lever to the lowermost position. Next, as the needle thread cassette is mounted from above in the cassette mount, the needle thread moves down while being guided by the thread guide members, and the needle thread between the second and third thread guide portions is automatically engaged with the thread tension regulator and the thread tension spring. The needle thread between the fourth and fifth thread guide portions is guided by the guide faces of the thread guide members and is automatically engaged with the thread guard of the thread take-up lever. When the needle thread cassette is completely mounted, the first and second resistance applying portions come into the released state so that the needle thread is fed out from the thread bobbin during the subsequent sewing operation.
In JP-A-55-81693, on the other hand, there is proposed a cassette type threading device for a sewing machine. This cassette type threading device is provided with a thread take-up lever travel region of an arm, a cassette mount disposed on the right side of the region, and a cover member for opening/closing the cassette mount. The needle thread cassette is removably mounted in that cover member. A thread tension regulator and a thread take-up spring protrude into the cassette mount, and a thread take-up lever travel space is formed in the left end portion of the cassette mount.
The needle thread cassette is provided with a bobbin housing portion and a pair of leg portions, and extends the needle thread, as fed out from the center of the bobbin, between the paired leg portions to form a free span. The cover member is opened by turning it 90 degrees forward and is closed after it is set with the needle thread cassette. At the action closing the cover member with the thread take-up lever being at the lowermost position, the free span of the needle thread cassette is automatically engaged with the thread tension regulator and the thread take-up spring. When the thread take-up lever is then raised, the needle thread is automatically engaged with the thread take-up portion of the thread take-up lever. Here, with the cover member being closed, the axis of the bobbin is directed in the horizontal direction and in the longitudinal direction.
In JP-A-7-24173, on the other hand, there is disclosed a needle thread cartridge, which is removably mounted on a cartridge mounting portion on the left side face of the arm head of a sewing machine. In the needle thread cartridge, a bobbin (or a thread bobbin) is retained in a case, a slit, into which the thread guard of the thread take-up lever penetrates, is formed in the wall portion of the case. In the case, there is provided a cartridge lever for supporting the needle thread to be engaged with the thread guard of the thread take-up lever. The cartridge is mounted in a cartridge mount irrespective of the vertical position of the thread guard of the thread take-up lever so that the thread can be engaged with the thread guard of the thread take-up lever.